Applicant's earlier application, Ser. No. 853,341, filed Apr. 17, 1986, now U.S. Pat. No. 4,705,540, describes polyimide membrane materials with exceptional gas permeation properties. The polyimide materials disclosed therein were compositionally prepared essentially from ortho-alkyl-substituted aromatic phenylenediamines with structurally rigid aromatic dianhydrides. Membranes from these materials offered moderate selectivities between gases. This level of selectivity has been improved in the present invention. The polyimide membrane materials described in the present application, therefore, find utility in a greater range of industrial gas separations.
Another of applicant's earlier application, Ser. No. 923,486 filed Oct. 27, 1986, now U.S. Pat. No. 4,717,394 demonstrated that a greater range of gas productivities could be achieved through the controlled addition of less chain rigidity than that found for the above application. This was accomplished, in part, through the use of mixtures of diamines which are rigid and substituted on essentially all of the positions ortho to the amine substituents and diamines which are essentially unsubstituted. The polyimide membrane materials described in the present invention can be prepared more efficiently by the use of methylene dianilines which incorporate both structural considerations described above.
U.S. Pat. Nos. 4,629,685 and 4,629,777 broadly disclose and claim similar compositions of matter as described herein for use in the electronics industry. They do not disclose any utility for gas separations.
U.S. Pat. No. Re. 30,351 and U.S. Pat. No. 3,822,202 (Du Pont) disclose aromatic polyimide gas separation membranes in which the molecular structure is such that the molecules in the polymer are unable to pack densely and, therefore, have high gas permeation rates. The membrane materials described in the present invention offer greater gas productivities.
U.S. Pat. No. 4,113,628 discloses aromatic polyimide gas separation membranes prepared from polyimide acid membranes.
U.S. Pat. Nos. 4,370,290, 4,460,526, 4,474,662, 4,512,893, and U.K. No. 2,102,333 disclose microporous aromatic polyimide membranes and the process from which they are prepared.
U.S. Pat. No. 4,486,376 discloses gas separation membranes made from microporous aromatic polyamide support treated with modifying agents.
U.S. Pat. Nos. 4,378,324, 4,440,643, 4,474,858, 4,485,056, 4,528,004, and U.K. No. 2,104,411 disclose gas separation membranes made from a microporous aromatic polyimide support coated with an aromatic polyamide acid or aromatic polyimide.
U.S. Pat. No. 4,378,400 discloses aomatic polyimide gas separation membranes in which the molecular structure is such that the molecules in the polymer can pack densely.